There are two main meanings of "capital":
1. Capital (as in money): The homonym for this meaning is "Capitol". This refers to a building, especially a government building. For example, the Capitol Building in Washington D.C.
2. Capital (as in a city): There isn't a true homonym for this meaning, as it's a different word altogether. You could argue that "capitol" is a homonym in this context, as it can refer to a city (e.g., "The capital of France is Paris"). However, this usage is less common and might be considered a bit informal.
So, to clarify, you need to specify which meaning of "capital" you're looking for.